Procedures have been developed for the purification of enzymes from human placenta that are lacking in patients with Gaucher's disease, Fabry's disease, Tay-Sachs disease and Niemann-Pick disease. The effects of enzyme replacement therapy in patients with these disorders is under investigation. Procedures have been developed for the diagnosis of patients with these disorders, the detection of heterozygous carriers of these genetic traits, and for the monitoring of pregnancies at risk for each of these diseases.